World's biggest storm of the year leaves a trail of destruction in Hong Kong, Macau and China's Guangdong province.

At least four people were killed in China's southern Guangdong province as a result of Typhoon Mangkhut, Chinese state television has reported.

Clean-up efforts were under way on Monday, a day after the world's biggest storm of the year made landfall in southern China and pummelled Hong Kong and Macau.

The storm has been downgraded from a typhoon to a tropical storm. Forecasters warned that strong winds and heavy rain will last until Tuesday.

Mangkhut passed over the northern Philippines on Saturday, where at least 65 have been killed and rescue efforts are under way in hopes of finding survivors in areas hit by landslides.

On Sunday, the storm made landfall in Guangdong province around 5pm local time (09:00 GMT), packing wind speeds of 162 km/h, while 10-metre-high waves battered the coastline.

More than 2.4 million people were evacuated from seven cities in the province before the storm's arrival.

Falling trees

Of the four fatalities in Guangdong, three died after they were hit by falling trees in Guangzhou while another was killed when a building collapsed in Dongguan.

In Hong Kong, Mangkhut made high rises sway and shattered windows. More than 300 were injured.

On Monday, commuters in Hong Kong had to clamber over fallen trees and piles of debris to get to work as life started getting back to normal.

"There were trees down all over the place, no cars, no buses," lawyer David Milligan, who works in Hong Kong's commercial hub of Central, told AFP news agency.

The gambling enclave of Macau, meanwhile, closed its casinos for the first time.

South China Morning Post reported 20,000 households were left without power on Sunday in the gambling hub while 1,280 fled to temporary shelters as severe flooding hit low-lying areas. Casinos have since reopened.